Social networks are the fundamental pathways for the transmission of values, behaviors, and disease. This project analyzes adolescent friendship, group affiliation, romantic relationship, and sexual partner network data to yield direct measures of the structure of the adolescent social world and to model the impact this structure has on health behavior. We focus on identifying cliques, their composition, and position in a network of cliques, thereby characterizing the macro-structure in which individuals are embedded. We propose to develop and estimate explanatory models of adolescent health behavior that use network variables to assess the effects of network position on health behavior. Special attention will be paid to health behaviors which carry specific short-term risk to adolescents or that are directly associated with transmission. In this project we intend to describe the structure of heterosexual contacts among adolescents and develop general behavior and attribute based mixing matrices necessary for mathematical models of STI and HIV transmission.